Heretofore, a hybrid electric vehicle and an electric vehicle use a high-power brushless motor. To control the brushless motor of the hybrid electric vehicle, for instance, it is necessary to accurately detect a rotation angle of a motor shaft. This is because, for switching control of energization to each coil of a motor stator, the rotation position of a motor rotor has to be accurately ascertained. In hybrid electric vehicles, specifically, drivability is apt to deteriorate due to motor cogging. Reducing the cogging is thus desired. It is therefore necessary to accurately switch the energization to each coil.
Herein, for detection of the rotation angle of the motor shaft in a hybrid electric vehicle, a rotation detector can be used to satisfy such functions as high-temperature resistance, noise resistance, vibration resistance, and high-humid resistance. The rotation detector is directly attached to the motor shaft in the brushless motor. As this type of rotation detector, for example, a variable reactance type rotation detector is used. This rotation detector includes a detection stator including an excitation coil and a detection coil, and a detection rotor placed near the detection stator and fixed to the motor shaft. The detection coil includes two coils arranged with a phase shift of 90° from each other. When an alternating voltage having a sine wave form is applied to the excitation coil, an induced voltage is output from the two coils of the detection coil through the detection rotor. Based on the output amplitude of this induced voltage, the rotation angle of the motor shaft (the motor rotor) can be detected.
As this type of technique, there is for example a rotary machine provided with a rotation detector disclosed in Patent Literature 1 listed below. In this rotary machine, the rotation detector is placed on the outside of a motor case and thus a zero point adjustment is easily performed, so that the rotation detector is less affected by magnetic noise of the motor. In this rotary machine, the detection rotor constituting the rotation detector is fixed on a motor shaft with a retainer such as a spacer and a nut. Furthermore, the detection stator constituting the rotation detector is arranged by winding a coil on a core.